Complete Chloroplast Genome Of The Host-plant Rhus Species Of Rhus Gall Aphids And Evolutionary Implications

Rhus gall aphids(Hemiptera: Aphididae: Eriosomatinae: Fordini)have complex life cycle with alterating between primary and secondary host plant,and they live on the primary host plant Rhus(Anacardiaceae)to induce galls well-known as the Chinese galls,which are economically important as medicines as well as sources of industrial tannin.Rhus gall aphids use only five species,i.e.Rhus chinensis,R.potaninii and R.punjabensis in East Asia,and R.glabra and R.typhina in North America,as Rhus gall aphids use only five species,i.e.R.chinensis,R.potaninii,R.punjabensis,in East Asia as their primary host-plants.In this study,we sequenced the complete chloroplast genome of the primary host-plant of Rhus gall aphids and P.chinensis from the sister genus Pistacia,and compared the genome characteristic with the Anacardiaceae species from Gen Bank.We constructed the phylogenetic tree of six genera from Anacardiaceae,and analyzed the relationship of Rhus apecies and other relative genera.The main research results are as followings:1.We obtained the complete chloroplast genome of the primary host-plant of Rhus gall aphids and Pistacia chinensis,and Rhus species content 159,187-159,984 bp in length,in which R.glabra has the longest cp DNA and R.chinensis with shortest cp DNA sequence,whereas P.chinensis contents 160,596 bp in length.The chloroplast genomes show a typical four-segment structure including a large single copy region,a small single copy regions and inverted repeat regions),which is consistent with most of other plants.The length in LSC region is 87,653-88,310 bp and18,522-19,090 bp in SSC region with the most difference.Whereas,IR region has the less difference in length with 26,496-26,598 bp in the Rhus species.2.The complete chloroplast genome contains 132 genes including 87protein-coding genes,37 t RNA genes and 8 r RNA genes,in which 16protein-coding genes,14 t RNA genes and 8 r RNA genes are located in IRs region.Among 113 individual genes,8 protein-coding genes,7 t RNA genes,4 r RNA genes are located in IR regions.The LSC region includes 60protein-coding genes and 22 t RNA genes while only 11 protein-coding genes and 1 t RNA gene are located in SSC region.3.According to the analysis of base composition,the average AT content of Rhus is 62.2%,and the average GC content is 37.8%.The content of AT is higher than GC,which is the same as other Angiospermae.The conservatism of the IR is higher than that of LSC and SSC while the content of GC in SSC area is the lowest and in IR region is the highest.There are5111 variable sites in the whole sequence,accounting for 3.4% of the total length of cp DNA,and 3783 in the LSC region accounting for 4.5% of the LSC region.Whereas,SSC region has 918 variable sites accounting for 6.4%of the SSC region,and 184 variable sites in the IR region,accounting for0.5% of the IR region,where the variaton is the least.4.The boundary analysis of the four regions showed that there was no obvious expansion and contraction in the genus Rhus species.The synteny of the cp DNA sequences indicated that there was the same gene order and no gene rearrangement happened in Rhus species.The gene ycf15 in IR region is between rps12 gene and trn V-GAC gene,however,this gene positioned between ycf2 gene and trn L-CAA gene in the species Pistacia chinensis,which is different with Rhus species.The boarder of the IR region is consistent with the genus Rhus.5.The structural characteristics of the cp DNA genome in the Rhus species were analyzed by comparing with these of other species in Anacardiaceae downloaded from Gen Bank.The results showed that the IR boundaries were greatly different at the IRb-LSC boundary,and the IR area in Spondias obviously conttracted.According to the mauve alighment,no gene rearrangement of large-area fragments was detected in all species,showing a collinear structure.The gene rearrangement of ycf15 gene occurred in the genus Pistacia,and some genes were lost in the genus Spondias and the trn G-UCC gene rearranged.The occurrence of collinear block inversion in the region between rps4 and psb D gene is an importantfeature in the genus Mangifera.The genomic comparsion between the genus Rhus and other Anacardiaceae species showed that coding regions were found to be more conservative than non-conding regions in the complete chloroplast genome.The IR region was more conservative than the LSC and SSC regions.The interval variation of rpl32-trn L gene in the genus Rhus is relatively higher than that of other species,and the hypervariable regions of pet N-psb M and ndh F-rpl32 are slightly different from other species.6.Based on all the protein coding genes,the phylogenetic analysis of the family Anacardiacea with Boswellia sacra and Commiphora gileadensis in Burseraceae as outgroups supported the monophyly of all the 6 genera,and that the genus Rhus and Pistacia were sister groups with a high support of100%.Rhus typhina is sister to R.glabra,and Rhus chinensis is sister to Rhus punjabensis and then grouped with Rhus potaninii as a cluster.7.The correlative test of the phylogenetic trees showed the significant coevolution between Rhus gall aphids and the primary host-plants Rhus species.